In the microfabrication by lithography, in recent years, the formation of an ultrafine pattern on the order of tens of nanometers is increasingly demanded in accordance with the realization of high integration for integrated circuits. In accordance with the demand, the trend of exposure wavelength toward a short wavelength, for example, from g-rays to i-rays and further to a KrF excimer laser light is seen. Moreover, now, the development of lithography using electron beams, X-rays or EUV light besides the excimer laser light is progressing.
Further, the microfabrication using a resist composition is not only directly used in the manufacturing of integrated circuits but also, in recent years, finds application in the fabrication of so-called imprint mold structures, etc. (see, for example, patent references 1 and 2 and non-patent reference 1).
In particular, the lithography using electron beams is positioned as the next-generation or next-next-generation pattern forming technology. Positive resists of high sensitivity and high resolution are demanded for the lithography. Specifically, increasing the sensitivity is a very important task to be attained for the reduction of wafer processing time. However, the pursuit of increasing the sensitivity with respect to the positive resists for electron beams is likely to invite not only the lowering of resolving power but also the deterioration of line edge roughness. Thus, there is a strong demand for the development of resists that simultaneously satisfy these properties. Herein, the line edge roughness refers to the phenomenon that the edge at an interface of resist pattern and substrate is irregularly varied in the direction perpendicular to the line direction due to the characteristics of the resist, so that when the pattern is viewed from above, the pattern edge is observed uneven. This unevenness is transferred in the etching operation using the resist as a mask to thereby cause poor electrical properties resulting in poor yield. Especially in the ultrafine region of 0.25 μm or less, the line edge roughness is now an extremely important theme in which improvement is to be attained. High sensitivity is in a relationship of trade-off with high resolution, good pattern configuration and good line edge roughness. How to simultaneously satisfy all of them is a critical issue.
In the lithography using X-rays or EUV light as well, simultaneously satisfying the requirements for high sensitivity on the one hand and high resolution, good pattern configuration and good line edge roughness on the other hand is now an important task, and it is required to resolve the task.
As a means for solving these problems, using a resin provided on its polymer principal chain or side chain with a photoacid generator is now being studied (see, for example, patent references 3 to 8 and non-patent reference 2). However, in the technology disclosed in patent reference 3, a mixed system comprising a resin provided with a photoacid generator and a dissolution inhibiting compound whose solubility in an alkali developer is increased by acid decomposition is used, so that because of the heterogeneous mixing of these materials, it was difficult to realize desirable pattern configuration and line edge roughness.
On the other hand, patent references 4 to 7 disclose a resin containing in its molecule both a photoacid generating group and a group whose solubility in an alkali developer is increased by acid decomposition. However, no aromatic ring group was introduced in the resin except for a cation moiety of the photoacid generating group with the intent to retain the transparency to 193 nm light in consideration of ArF and ArF liquid-immersion exposure. In the lithography using electron beams or EUV light, it is generally contemplated that the aromatic ring moiety of, for example, polyhydroxystyrene or the like when exposed to electron beams or EUV light emits secondary electrons, by which the photoacid generator is decomposed to thereby generate an acid. Therefore, it does not seem quite proper to state that the sensitivity of the resin to electron beams, X-rays or EUV light is satisfactory.
Moreover, patent reference 8 and non-patent reference 2 describe a terpolymer obtained from hydroxystyrene, an acrylate containing an adamantyl group and an acrylate containing a photoacid generator. Patent reference 9 discloses a resist comprising a resin containing a repeating unit sensitive to high-energy rays or heat that generates sulfonic acid at a fluorinated terminal of its side chain in order to enhance the high resolution, iso/dense bias and exposure margin of the resist.
However, with respect to a resin containing a photoacid generating group and an acid-decomposable group in its side chain, the structure of the photoacid generating group is important, and it has been difficult for the above prior art to simultaneously satisfy the requirements for high sensitivity on the one hand and high resolution, desirable pattern configuration and desirable line edge roughness on the other hand in the lithography using X-rays or EUV light.
Furthermore, depending on the structure of the photoacid generating group, an unsatisfactory aging stability of resist has been experienced.
As apparent from the above, the current situation is that any combination of prior art technologies known to now cannot simultaneously fully satisfy the requirements for high sensitivity, high resolution, desirable pattern configuration, desirable line edge roughness, resist aging stability, dry etching resistance and the like in the lithography using electron beams, X-rays or EUV light.